docs: github action setup instructions

[jay-babu]

I can figure it out but would be nice to have some instructions on how to setup this up to work with github action as a validation step to ensure the sql is formatted correctly.

bonus would be a step to format and fix it as part of the action

[darold]

Execute prove at command line to run regression test.

[jay-babu]

Execute prove at command line to run regression test.

@darold not quite following. I meant if people wanted to use pgFormatter in their own CI setup, some instructions on how to do it would be nice

[darold]

Added a CI action scripts to validate changes and could be used as example for own CI setup,.